The term die-cast model car generally refers to any toy or collectible model car produced by using a die-casting method. For many years, the bodies of pre-assembled and commercially sold model cars have been made of metal, usually a durable zinc alloy (Zamak) that is both easily cast and hand-worked and also structurally rigid, with plastic, rubber, or glass used for details.

Die-casting has been preferred by most model car producers above all other kinds of processes due to the quality of the finished goods and also the ease of manufacture. It is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. Zinc is arguably the easiest metal to cast, as it has a relatively low melting point of 385 degrees C (725 degrees F), high ductility, and high impact strength, and it is easily plated. It is also economical for small parts, offers high dimensional accuracy, and promotes long mold life (up to one million “shots” or castings).

However, there are challenges with zinc. When the molten zinc is forced into the mold cavity in a split second, as it is during die-casting, the molten metal cannot flow smoothly if the passage is uneven and inconsistent, thus causing turbulence in the molten material. This turbulence traps air and makes the casting porous, an unwanted result brought about by air pockets and void space inside the molded material. The phenomenon is more likely to happen if the molten material has to transition from a large area of the casting, such as the model car’s roof, down into a narrow passage, such as the A-pillar, then emerges again into a large area, such as the model car body. When the passageway between these two areas is uneven and inconsistent, porosity is a real problem.

Porosity arising because of turbulence inside a die-cast piece can cause weakness of the material, which can help make the finished piece brittle and fragile. The structure becomes less stable because the density of the metal particles melded together is not balanced due to the small voids of space within. In most cases such porosity is not outwardly visible, but when the die-cast piece is painted and then oven-baked, the heat causes the gas in the pores to expand, which causes micro-cracks inside the part and exfoliation of the surface. Tiny bubbles in the form of rashes appear on the painted surface and the piece must be scrapped. In order to avoid the problem, mold-makers create bridges in large open areas such as the windscreen to help the molten material flow smoothly.

Slots and vents are also made as dead-ends so that the flow will not be interrupted. Later, they can be opened through machining, or the voids can be simply painted black, depending on the quality of the model.

Die-casting is an ideal process to produce low-cost mass-market model cars when the body shape is small and simple. In those cases, the A- and B-pillars are often made disproportionally thicker in order to ease the flow of molten material during casting. Slots and vents are also typically closed off to avoid any uneven flow.

When the first die-cast model cars appeared in the market before World War II, they were made as toys with simple body shapes and no interior, and were mainly intended for children to play with. By the 1980s, it was apparent that adults were purchasing many die-cast model cars as collectibles, and not just as toys for children. The later die-cast model car body made of zinc metal emerged as easy to cast and rigid enough to withstand heavy impact, and able to be cast with a metal mold in mass quantity quickly and accurately and at low cost. The weight of the metal body also gave the model a good, heavy feel in the hands.

In the late 1980’s, China opened its doors and people started to invest in the country because of its low labor cost. Model-car manufacturing gradually moved to China as the nation became the world’s factory, its labor costs only a fraction of those in western countries. The model makers could afford to hire thousands of workers to make sophisticated and high quality model cars, and still be able to export the models at very low price. The quality level and detail, particularly in 1/18th scale, started to move to a higher level due to competition and increasing buyer expectation. Collectable model cars increasingly became more complicated to manufacture, with the parts count reaching into the hundreds for each model, requiring hundreds of workers in the production line to create and finish each and every single piece of the model.

While die-casting remains popular in manufacturing low-cost mass-market model cars, it is no longer an ideal production method for collectable models that must have body shapes that are true to scale down to the smallest detail. As the slots and vents must be closed off during die-casting to avoid the uneven flow of molten material inside the mold, high-end collectable models will require these slots and vents to be true open passages, to remain accurate to the actual car. Thus they must be cut open by a milling machine, one by one and bit by bit, then manually trimmed at the edges until the opening is clean. This is a very labor-intensive process that adds substantially to the production cost.

When a model of a real car is made perfectly true to scale, some body parts, such as the A- and B-pillars, are usually very slim, which can cause the casting issue mentioned earlier. Porosity is one thing that can never be eliminated completely, and the product engineers are always battling to overcome the problem.

Another issue with die-casting is that during the high-pressure “shot,” a small parting line will form on the casting surface that results from the gap between the two halves of the mold. These tiny, hard-metal parting lines protrude from the body’s surface and can only be removed with a metal file, after which the surface is further smoothed manually by sand paper. On mass-market, toy grade models, the parting lines on the body are left untouched and go straight for paint coating in order to keep down the labor cost as much as possible. However, on collectable die-cast model, parting lines on the body surface must not exist. Therefore, intensive surface polishing has to be done manually before painting. Workers carefully remove the parting lines with a file and then polish the area with sandpaper. This process cannot be done partially; the whole car body must have a perfect smoothness in order to achieve an even glossiness to the paint. Therefore, each and every single body surface must be thoroughly polished by hand, and at a different intensity on different areas, to avoid any over-polishing on edges and creases. Otherwise the original shape of the body may be compromised.

And no matter how careful the workers polish the model body, the edges and creases inherent to the original car design will be rounded-off slightly during polishing. Thus, with zinc die-casting, the finished model can almost never replicate the original body shape perfectly. Moreover, the metal dust created from the polishing process can cause skin allergies in the workers. So, not only is the polishing process very labor intensive and costly, it is also the kind of work that most employees dislike.

These are some of the reasons why we are seeing fewer and fewer high-end collectable die-cast model cars launched into the market in recent years. It has become very expensive to produce die-cast models as the labor cost has increased ten-fold over the last two decades, and thus the selling price becomes so high that even diehard collectors are slowly abandoning the hobby because they simply cannot afford to collect anymore. Only toy quality die-cast model cars have a future in the market in the years to come, as they can still be sold at an affordable price as gifts or playthings for children rather than as collectibles for adults.

To counter the increased labor costs, many model makers have turned to resin to replace die-cast metal for the body. Resin models can be made very nicely and with minimal tooling investment, although the manufacturing cost for each one of them is much higher. And due to the nature of resin material, the models can be fragile, breaking or deforming easily when they are not handled with care. That’s because resin doesn’t flex, and also isn’t as rigid as a die-cast body. Because of these weaknesses, resin models are mostly made as sealed bodies with no openings. Because resin is brittle and breaks easily, it is not possible to install the small hinges that movable panels require without risking a failure of the resin after just a few openings and closings.

AUTOart has decided that instead of resin, it will transition to a composite model that uses injection-molded ABS composite parts. Modern injected ABS composites have proven to be an ideal material to form the body of a model car. Compared to a die-cast zinc metal body, injected ABS composite material surfaces, with the correct formulation, are smoother and the bodylines and creases are sharper. The openings for vents and holes are also reproduced more cleanly, and the panels can be much thinner when rendered in ABS composite material than in zinc alloy. That makes the finished body closer to the true scale gauge of real car bodies. AUTOart’s composite models are not sealed, but have full array of working closure panels, including the doors on all models and the engine bonnets on many subjects.

Of course, the new material also presents challenges. A body made of ABS, as with a real car made of thin-gauge steel or aluminum, is generally not rigid enough alone. It tends to flex and deform under twisting or compression. If such a model is made featuring opening doors, the doors will pop loose under flexing and they will not close properly once the body is slightly deformed. In order to make the whole composite body rigid enough, we pair it with a die-cast interior that is designed to support the body in all the areas that need to be strengthened. With a metal interior, the whole composite body becomes rigid, which is no different than the concept behind a die-cast metal body—or, indeed, many real cars that use internal structures to give the body rigidity.

The reinforced composite body will not flex easily and will never deform, and doors and bonnets will always open and close in the same position. Also, as a bonus, the finished model’s door gaps are finer when rendered in composite material than in die-cast zinc.